Reversible Redox-Based Optical Sensing of Parts per Million Levels of Nitrosyl Cation in Organic Solvents by Osmium Chromophore-Based Monolayers

Exposure of an osmium(II)-based monolayer on glass to organic solvents containing 0.36-116 ppm of NOBF4 results in one-electron transfer from the covalently immobilized complexes to the inorganic analyte with concurrent optical changes. The NO+ induced oxidation of the monolayer can be detected optically with an off-the-self-UV/vis spectrophotometer (260-800 nm). The redox-based NO+ detection and quantification system can be reset with water within ∼20 s for at least 40 times. The reaction of the monolayer with a THF solution containing 5 ppm of NOBF4 follows pseudo first-order kinetics in the monolayer with ΔG#doubledagger#298K = 21.5 ± 0.7 kcal/mol, ΔH#doubledagger# = 9.5 ± 0.3 kcal/mol, and ΔS#doubledagger# = -40.6 ± 1.1 eu. The monolayer structure and properties have been resolved by electrochemical measurements and synchrotron X-ray reflectivity measurements in combination with density functional theory calculations (B3LYP/SDD level of theory)